Re: [PATCH v2 01/15] PCI/MSI: Forward MSI-X vector enable error code in pci_alloc_irq_vectors_affinity()

Logan Gunthorpe
2020-06-03T15:48:35Z

On 2020-06-03 5:44 a.m., Piotr Stankiewicz wrote:
> When debugging an issue where I was asking the PCI machinery to enable a
> set of MSI-X vectors, without falling back on MSI, I ran across a
> behaviour which seems odd. The pci_alloc_irq_vectors_affinity() will
> always return -ENOSPC on failure, when allocating MSI-X vectors only,
> whereas with MSI fallback it will forward any error returned by
> __pci_enable_msi_range(). This is a confusing behaviour, so have the
> pci_alloc_irq_vectors_affinity() forward the error code from
> __pci_enable_msix_range() when appropriate.
>
> Signed-off-by: Piotr Stankiewicz <piotr.stankiewicz@intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> ---
> drivers/pci/msi.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
> index 6b43a5455c7a..443cc324b196 100644
> --- a/drivers/pci/msi.c
> +++ b/drivers/pci/msi.c
> @@ -1231,8 +1231,9 @@ int pci_alloc_irq_vectors_affinity(struct pci_dev *dev, unsigned int min_vecs,
> }
> }
>
> - if (msix_vecs == -ENOSPC)
> - return -ENOSPC;
> + if (msix_vecs == -ENOSPC ||
> + (flags & (PCI_IRQ_MSI | PCI_IRQ_MSIX)) == PCI_IRQ_MSIX)
> + return msix_vecs;
> return msi_vecs;
> }
> EXPORT_SYMBOL(pci_alloc_irq_vectors_affinity);
>

It occurs to me that we could clean this function up a bit more... I
don't see any need to have two variables for msi_vecs and msix_vecs and
then have a complicated bit of logic at the end to decide which to return.

Why not instead just have one variable which is set by
__pci_enable_msix_range(), then __pci_enable_msi_range(), then returned
if they both fail?

Logan